Electric oven heating system



June 8, 1948. F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM 9 Sheets-Sheet 1 Filed Nov. 3, 1939 F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM June 8, 1948.

9 Sheets-Sheet 2 (D-Om:

Filed Nov. 3, 1958 June 8, 1948.

Filed Nov. 5, 1959 F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM 9 Sheets-Sheet 3 June 8, 1948. F. H. M CORMICK I ELECTRIC OVEN HEATING SYSTEM 9 Sheets-Sheet4 Filed Nov. 3, 1959 LLO F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM June 8, 1948.

.9 Sheets-Sheet 5 Filed Nov. 5, 1939 n p u 1 5 June 8, 1948. MCCORMICK 2,442,90Q

ELECTRIC OVEN HEATING SYSTEM Filed Nov. 3, 1959 9 Sheets-Sheet 6 9 Sheets-Sheet 7 Filed Nov. 3, 1939 IQUIIICII ll ATTORNEY5 June 8, 1948-.

Filed Nov. 5, 1959 F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM 9 Sheets-Sheet 8 Zia (@1- gin/g TOR.

BY a 2 E ATTORNEYS June 8, 1948. F. H. M CORMICK ELECTRIC OVEN HEATING SYSTEM 9 Sheets-Sheet 9 Filed NOV. 5, 1939 Patented June 8, 1948 UNITED STATES ()FF I ELECTRIC'OVEN HEATING SYSTEM Francis H. McCormick, Dayton; flhio, assignorto General Motors Corporation; Dayton, Ohio, a

corporation of Delaware Application November 3, 1939;.- Serial No.' 302,7 28

, in electric stoves.

This application is a continuation in" part of my copending' application Serial No. 208,143, for

*2 an electric surface-heater-form'ed of-a plurality of concentric rings in which the outer ring-has a greater density of-wattage'per square inch than the inner ring.

5 The problem-of providing uniform heat dis- Domestic appliance, filed May 16, i938 (now tribution for awidevariety of food loads-inan abandoned). oven ispe'rpetual and continuing. Appa-rently t has been found that a more uniform -temthere'is noperfectsolutiorr'tothe-problem; but perature will be attained in an oven by supplying impro are a y possible anddsifablethemajor portion of the heat at the bottom'and Itiscustomary 'pl c mainheatins'unit i a small amount of evenly'distributed heat at the th'"b0tt0m"0ffthe OVBYI- ThiSJhOWBVBIE has a top of the oven. The space Within'the oven is tendency to-make 'thepdrtiorr of the oven' immade more usable by providing the broiling mediately' above the-heating'-unittoo-hot. "Variheater at the top of th oven, If separate h t ous forms of ba'filesor heat shields over'the lower are provided in the top of the oven "for broiling heating unit ave beentried but I find these for baking the heaters will interfere to preforms ratheriinjefiebtive tend p vent either heater from providing the desired the heat in 15013130111 0f the Ovenuniiorm distribution. t is an object of my invention toprov'ide' a t is an object of my invention to'providean heatingarra'ngement for an electric oven= which arrangement for a heater in the'upper portion W provide a more even tr ut n at of the oven which will cause the heater to supply a particularly will pre en e u oft e heatuniformly at a sufficient rate for broiling bottom Q being baked 01111116- lowrsh'elf in when desired or at a much lesser rate'when it the Ovenis desired to us the ov f baking Itis'another object of my invention to provide I have found that th inn portion of" t an-improved baflle arrangement for-thelh'e'ater electric surface heaters tends to become 'mu'eh "in-the bo'ttomof 'the'oven'whichwill shield the Warmer than the outside portion of such" heaters, shelvesvfrom radiant heat afiwprovide a even though ithas been customary to provide e fi yd t buted circulationbf'hbt air the heat uniformly ov th urface of the *in the-oven" but which "will' avoid thetrapping heaters. One reason for this is that the outer 3o Q beneath 7 portions of such heaters are exposed'to relatively t has been'foundi th'ewilllL Order C001 air as Well as cooler portions of the range form -temperaturedistribution over-an area adadjacent the heaters. Convection currents at *J e g unit of radiant yp it is deth outer edges of t heaters carry-aWay-heat -si-rable :to reduce 'the heat intensity adjacent the from the outer portions of the surface heaters -"fi e' heating unit and to increase the with considerablerapidity. The inner portions 85 heat'intenislity M the edg-portions bf the'heating of theheaters are separated from the convection unit- This true'vfor baking and: bromng currents of cool air as well as cooler portions of W assurfaceheat 'un the range adjacent the heaters by the outer porlther'efolfe another Objectbf y i ention tions of the heaters, and the hot air rising from to pmvide an improved arrangement oftheheatthe outer portions of the heaters. This condition iflgimeans i e OttOm and top of the'oven to is frequently d Worse b reason of theiact increase heat intensity at the edges of-thehe'ating that cooking utensils often have "concave bottoms means 3nd eSpe5fanY at thelf-rom and real" Edges and thus tend to make contact" only on the out 701'deri't0 "Obtain "more uniform temperature side of the heater and ordinarily remain out of fiistributmn- I contact on the inside or center."'1his causes most I It is 351115 anotheTWbJ-ect mYmVQIitiOII' 130 of the heat to be conducted directly from the providewheafing'meanswithan'improvd-supheater to the utensil or to the outer portion thereportv :the insulators of 515119 9186171 16 esistance of, while the inner portion is forced to employ meanssome less efiicient manner of heat transmission. "Further Objects and'advantages 0 'th p It is therefore an object of my invention to invention'will be apparent from the'followingdeprovide an electric surface heater in which the fi 'pfi reference beinghad $039116 p yheating intensity increases from theinner poring drawings, wherein apreferredf form'of the tions to the outer portions of the surface heater. present invention 'is 'clearl'y shown.

It is another object of myinventicn to'pro vide In"the"drawings:

Fig. 1 is a perspective view of an electric stove embodying my invention;

Fig. 2 is a fragmentary rear view of an electric stove embodying my invention;

Fig. 3 is a complete wiring diagram for an electric stove shown in Figs. 1 and 2;

Fig. 4 is a wiringdiagram of the oven heating system together with its control switch shown in off position; i

Fig. 5 is a wiring diagram of the oven heating system with the control system shown in low heat position;

Fig. 6 is a wiring diagram of the oven heating system with the control switch shown in baking position;

Fig. 7 is a wiring diagram of an oven heating system with the control switch shown in broiling position;

Fig. 8 is a vertical transverse sectional view through the oven, both heating elements and the bafile;

Fig. 9 is an enlarged sectional view of a portion of the lower heating means shown in Fig. 8;

Fig. 10 is a sectional view through one of the insulators taken along the lines ll0 of Fig. 11;

Fig. 11 is a sectional view of a portion of the heating means shown in Fig. 9 taken along the lines llll of Fig. 9;

Fig. 12 is a plan view of one of the heating units for the oven, the upper and lower heatin units of which may be made identical;

Fig. 13 is a modified form of the heating means shown in Fig. 12, made so as to provide a greater amount of heat at all of the edges;

Figs. 14 to 19 inclusive are diagrammatic representations of modified forms of wiring construction;

Fig. 20 is an enlarged view of a portion of Fig. l; and

Fig. 21 is a vertical cross-sectional view taken along the center of the cable channel 34.

Briefly, I have shown an improved electric stove or range which is simple and desirable in construction. It is provided with surface heaters having two concentric heater rings and the outer heating ring has a sufiiciently greater heating capacity to provide a greater heating effect per square inch than the inner ring. Preferably the outer ring has at least twice the heat: ing energy of the inner ring. For high heating both the rings are energized to their full capacity,.while for medium heat the inner ring only is energized at only one-half voltage and provides a heating effect equal to about one-half of the full effect of the inner ring and about one-fourth of the full heating effect of the outer ring. This heating arrangement provides a greater heating effect upon the outside ring where the cooking utensils normally contact and it also provides a better selection of heating rates for normal cooking requirements. I have found that the heating capacity for medium heat should be considerably less than one-half the high heating rate and that the low heating rate should be further reduces the actual voltage upon the upper heater. By this arrangement I can use an evenly distributed heater in the upper portion for both broiling and baking in order to get uniform heat distribution for either broiling or baking. I also provide a preheating arrangement by which both upper and lower heaters are operated at full voltage and maximum capacity.

Referring now to the drawings and more particularly to Fig. 1 there is shown an electric range including a range shell 20, preferably coated with porcelain inside and out, which is provided with a cooking top 22 having an integral back panel 24, all of which is coated with porcelain on both sides. The top is provided with four surface heaters 26, each provided with an outer heating ring 28 and an inner heating ring 30. These heating rings form the surface heaters and are made of different sizes and different heating rings.

For example, the inner ring may have an outer diameter of 4 /2" and an inner diameter of 2%" and an upper surface area of about 12 square inches. Preferably it has a rate of 400 watts at full voltage giving it a heating density of about 33 watts per square inch. The outer ring preferably has an outer diameter of about 6 /2" and an inner diameter of about 4 /2" providing an upper surface area of about 1'7 square inches. Preferably this outer ring has a heating ring of about 800 'watts providing a heat density of about 50 watts per square inch. This provides about 50% greater heating density in the outer ring than in the inner ring. This counteracts the tendency of surface heaters to get much hotter on the inner portions than the outer portions. I find that cooking utensils often have concave bottoms causing them to contact upon the outside ring and usually fail to make contact with the inside ring. Thus the heat will be removed from the outside ring much more easily than from the inside ring and the greater heating density provided by the outside ring will therefore compensate for its greater rate of heat transfer to keep both rings at about the same temperature.

If desired, the surface heaters may have more than two concentric heating rings with the inner ring having the least heat intensity and the outer ring having the greatest heat intensity. In such a surface heater, the intermediate heating rings preferabl have an intensity intermediate the heat intensity of the inner and outer rings. If there are more than one intermediate ring their heat intensity may be graduated so that the heat intensity of the heaters increases progressively from the inner ring to the outer ring. Other types of surface heaters may also be made so as to provide greater heat intensity upon the outer edges thereof than upon the inner portions thereof. For example, surface heaters of the spiral coi-l type may have their coils widely spaced in their inner portion and closely spaced in their outer portions to provide greater heat intensity in the outer portions. The spacing of such coils preferably progressively decreases from the inner portions to the outer portion to provide a rogressively increasing heat intensity. 7

The bottom of the surface heaters 26 are separated from their switches by a switch shield 32 located beneath the top cover 22 and extending generally downwardly at an angle from its front edge. A U-shaped channel 34 is connected to the shield and conductsthe necessary wiring from.

the surfaceheatersto theservice: heater switches 84,J86,:-36 and.88. These surfaceheater switches formpart of a switch channel. assembly which includes the switch channel. 38 which. is'fastened by. screws atits opposite ends .to' .the front portions of the range shell 20. The switch channel has the surface heater switches 84, 85, 36 and 88 fastened to its rear face and the operating shafts of-theswitch extend forwardly through the switch channel sothat they. may be provided with switch handles after a switch panel iswplaced over the swtich. panel assembly. The switch channel assembly is also provided with a fuse and fuse receptacle member M1. The wiring from the switch channel assemblyis grouped together in sort of a flexible conduit 42 which extends rearwardly through a channel 44 located immediately .beneath the cooking top 22 and extending from the fronttothe back of the range.

- Directly beneath the surface heating units is a large warming drawer 48 and beneath this large'drawer 63 is an electric heater called a worming unit 48 by which. the large drawer may be =-heated forkeeping food which has already been-prepared at a desirable temperature or it may be used to warm dishes prior to serving of a meal.

The walls .of the oven proper are provided by an oven shell 50 which fits into the front of the rangeshell 20. with insulation and through its rear wall extend the plug receptacle 52 and 5d. The upper oven heating unit 55 plugs directly into the upper receptacle 52 while the lower oven heating unit 58 plugs into the lower receptacle 54. These upper and lower oven heating units are identical except for the fact that the lower heating unit is provided with an evenizer baffle 68 for the purpose of balancing the distribution of heat through the oven. 1 Each of the oven heater units are of the opencoil type. and are designed to provide a uniform heat distribution over their entire area. They have arating of 2060 watts at full voltage.

The oven heating units are controlled by an oven switch 52 having a knob located upon the frontface of back panel 24 and the remainder of the mechanism located upon the rear of the back panel 2I-. As will be further explained in connectionwith Figs. 4 to '7 this switch provides an on position, a preheat position, in which both heatersare energized by full voltage to give rapid heatingyand a bake position in whichthe lower heater is operated at'full voltage andthe upper heater is connected inseries with the resistance and the two are operated at one-half voltage in order to provide a small evenly distributed amount of heat at the top of the oven to provide uniform heating for baking purposes. A broiling position is also provided in which the upper oven heat unit is operated alone for broiling purposes.

At one side of the oven switch 62 is the oven temptrature control G l which in reality is a thermostat which. operates a set of switch contacts to control the supply. of current to the oven heating units. .At the side of the oventemperature control 84' there is provided a timer clock E8 which maybe used tostart and stop the energization of the .oven heating units at any particular set time. At the side of .the'clcck S6 is a time signal 68 which may be set to ring a bellat any particular time desired. On the other side'of the oven switch 62 sis an oven vent .10 which permits air, odors and vapors to. escape from the oven. Atthe side oi-this vent l0. is-a warmer switch 12 beneath which-is asignal light 14 which islighted when- The oven shell '59 is surrounded everthe. upperunit is-in: operation. Belowthe signal light "is an appliance receptacle 16 which may. be. used. as; an outlet for an .electricteakettle or percolator .or the like.

Theexternal resistance .78 for use with the upperv oven heating unit-.5 3 during baking operations is located upon the backof the range and like the other electrical parts is connected to the line terminal blocktll which is located adjacent the bottom of the rangeto which the supply electric conductors are. connected. Preferably the range operates upon a three-wire -120, 230-240 volt distribution system. The electrical connections shown in Fig. 2 at the rear of the range are concealed by the rear cover 82 of the range.

Referring now more particularly. to Fig. 3 which shows thewiring system of the range, the line terminal block illlis shown connected to the surface heater switches 84, 88, 36 and 88. The connection between these switches and the line terminal block 86 is made by the conductors which pass through the channel M provided for them. The switch 84 is connected to the left front surface heater 25 which includes the outer ringeshaped heating member 28 and the inner ring-shaped heatingmember 36. The switch 8:! includes a knob t l provided with a pointer t6. Four positions oif, high, medium and low are indicated upon the switch panel.

Theknob 94 is connected to a shaft 98 provided with cams [02, Hi l and [$5. The cam I82 operates the contact H355 which makes engagement with the stationary contact I lllfor supplying current to a connection which connects with one end of each of the heating members 28 and 3G. The other end of the heating member 38 is connected to the stationary contact H2 which is adapted to be contacted by the movable contact H4, which in turn is connected to the middle wi e of the terminal block. The other end of the heater 28 is connected to a double stationary contact H6 having a contact H8 adapted to be engaged by the movable contact I28 which is connected to one of the outside conductors, while the second contact E22 is adapted to make contact with the movable contact H4 connected to the middle wire.

The other switches are connected to the left rear, ri ht rear, and right front surface units in the same manner as is the switch 84. However, t re switch 84 is shown in the off position. with the contact I03 away from the contact its and the contact H4 away from the contact H2. In this position, since only one conductor is connected to the supply line, no current can flow through any of the heaters.

When the knob 94 of the switch is turned to the high position, the cam 982 will be turned so that its point of contact with the contact 5538 will be changed from its high portion to its low portion. This will permit contact .698 to make contact with the contact H6. The cam lilo. will also be rotated but the contact He will remain upon the high portion of the cam. The cam let will also move one-fourth turn in a clockwise direction so that the contact of the cam with the contact 225 will bechanged from the high portion of the cam to the low portion of the cam. This will cause the contact I20 to engage the contact H8. Thus when the switch 84 is turned to the high position, the current from one of the out side lines will flow through the contacts l2t and H8 to the heater 28. Current from the middle supply line will flow through the contacts M and H2 to the heater30. Current from the other outside supply line will flow through the contacts I08 and H to both the heaters 28 and 30. Thus the current flowing through the outside ring heater 28 will flow from one outside supply line to the other while the current flowing through the inner heater 30 will flow from the middle supply line to one of the outside supply lines. Thus the outside heater 28 will be supplied with the maximum voltage for which it is designed, namely, 230-240 volts, while the inner ring'heater 30 will be supplied with itsmaximum voltage namely 115 to 120 volts. The switch 86 is shown in the high position.

When the knob 94 is turned to the medium position the contacts I08 and H0 remain closed and the contact H4 remains in engagement with the contact II2. However, the contact I20 is again moved out of engagement with the contact I I8 so that no current can flow through the outside ring heater 28. Full voltage, howeven'is applied to the inner ring heater 80. The switch 86 is shown in the medium position.

In the low position, the contact I08 remains in contact with contact IIO, but the contact H4 is moved out of engagement with the contact H2 and into engagement with the contact I22, because in this position the low portion of the cam I04 makes contact with the contact II4. In this low position, the contact I20 remains out of contact with the contact I I8. Thus, current from the middle conductor of the three-wire system passes through the contacts II4 and I22, which forms a portion of the double contact member H6, to the outer ring heating member 28, from which the current flows through the contacts H0 and I68 to one of the outside conductors of the three-wire system. Thus when the switch 84 is in this position only one-half full voltage is applied to the outer ring heater 28 and only one-fourth the full heat rating is obtained from the heater 28. The switch 88 is shown in the low position.

Also connected to the three-wire conductors extending from the line terminal block 80 is the warmer unit 48 which is controlled by the warmer unit switch I2. The conductors to the warmer unit 48 are shown as entering an aperture I26 in the rear wall of the range in Fig. 2 and make connection with the warmer unit 68 as shown beneath the large drawer 46 in Fig. l. The warmer unit is connected to the middle connection and one of the outside connections of the line terminal block 80 so that the Warmer unit operates on 115-120 volts. The oven temperature control 64 includes the double contacts E28 connected by conductors I80 to the timer clock 66 which in turn connects to the two outside conductors connecting to the line terminal block 80. The double switch contacts I28 are connected by conductors to the binding posts I 32 and I34 of the oven switch 62. The oven switch 62 is provided with a third binding post I 36 connected to the external resistance 18 which in turn is connected directly to the middle conductor connected to the terminal block 80.

The upper left front and the upper right rear binding posts I88 and I40 of the oven switch 62 are connected to the terminal 54 which connects to the lower oven heating unit 58. The left rear and right front binding posts I62 and I44 of theoven switch 62 are connected to the upper terminal 52 to which is connected the upper oven heating unit 56. The signal light I4 is connected to the conductor which is connected to the bind-- ing post I42 and is also connected to one of the terminals of the appliance receptacle I6 whicli in turn is connected to the middle conductor connected to the line terminal block 80. The other conductor of the appliance receptacle is connected to a fuse I46 which in turn is connected to one of the outside conductors connected to the line terminal block 80.

Referring now more particularly to Figs. 4 to 7 inclusive, there is shown the oven switch I02 in its four positions connected diagrammatically to the upper and lower oven heating units 56 and 58. In Fig. 4 the oven switch is shown in the ofi position as indicated by its control knob I50. The knob I50 is connected to one end of a cam shaft I52 which is provided with cams I54, I56, I58, I60 and I62 arranged upon the shaft I52 in order. The cam I56 is contacted by the contact member I64 which is adapted to make contact with the stationary contact I66 connected to the external resistance I8. The high portion of the cam I54 is in contact with the contact I64 at all times except when theknob I50 is turned to bake position as is shown in Fig. 6, at which time the contact I64 will be engaged with the low portion of the cam I50 to permit the contacts 44 and I66 to close.

, The cam I56, which is next in line, is engaged by the contact I68 which is adapted to make contact with the stationary contact I10 forming a part of a contact bar I'I2 which it shares with the stationary contact I'M. The high portion of cam I56 remains in engagement with the contact I68 keeping it in open position in the ofi" and "high positions, but in the preheat and baking positions contact I68 is engaged with the low portion of the cam I56 so that it makes contact with the stationary contact I70. The contact I68 is on the same side of the shaft as the contact II6 which is operated by the cam I60. When the knob I50 is turned to the preheat and bake positions the contact I76 is in contact with the low portions of the cam I60 so that the contact I16 is in engagement with the contact I'I4 upon the contact bar IIZ-at the same time when the contact I68 is in contact with contact I'I0 upon the other end of the contact bar I12. However, in the broil position the contact I16 is also in engagement with the low portion of the cam I60 so that it remains in engagement with the contact bar I'I2 while the contact I68 is moved away from contact bar I'I2 by the high portion of its cam I56.

Upon the otherside of the cam shaft I52 is another contact bar I80 provided with a stationary contact I82 adapted to make contact with a movable contact I84 which is operated by the cam I58. The other stationary contact I86, upon the contact bar I80 is adapted to be contacted by the movable contact I88 which is operated by the cam I62. In the preheat position the low portion of the cams I58 and I62 are in contact with the movable contacts I 84 and I 88 so that both of these contacts are in conducting relation with the contact bar I80 which is connected to one outer conductor connected to the line ter minal block. When the knob I 50 is turned to the bake position, the cam I 58 has its high portion in engagement with the movable contact I84 thus disengaging it from its stationary contact I82 upon the contact bar I80. The cam I62, however, has its low portion in engagement with the movable contacts I88 so that it remains in contact with its stationary contact I86. In the broil position of the knob I50, the situation is reversed and the low portion of' the cam I58 engages the movable contact I84 permitting it to contact the stationary contact I82 while the high portion of the cam I62 is engageable with the movable contact I88 to separate it from its stationary contact I06.

Thus it will be seen in the off position all of the contacts are separated from their cooperating contacts to prevent any energization of the heaters. In the preheat position one of the outside conductors connecting to the line terminal block is connected through contact bar I12 with both the movable contacts I68 and I16 to supply electric energy at full voltage to both the upper and lower heating units 56 and 58. The upper oven heating unit 56 is also connected through a common conductor I-Qfi to the movable contact I84 and through the common conductor bar I80 to the other side of the three-wire system connected to the line terminal block. The lower oven heating unit 58 is also connected to the movable contact-I88 which engages the common contact bar I80 connected to the other outside conductor of the three-wire conducting system connected to the line terminal block 8B. Thus it will be seen that in the preheat position the heating units have one end connected to the common contact bar I12 while the other end is connected to the common contact bar I88.

In the bake position shown in Fig. 6 one of the outside conductors is connected to the common contact bar I12 and through this bar to the movable conductor I68 and to the lower oven heating unit 58 which in turn is connected through the movable conductor I88 to the other common contact bar I80. In this control position the common contact bar I12 is also contacted by the movable contact I16 which connects to the upper oven heating unit 56 which in turn is connected to the common conductor I90 which is connected to themovable contact I64-which in turn engages the contact I66 connected to the external resistance 18 to apply the 115-120 volts to the upper oven heating unit 56 and the resistance 18 so that the heat output of the upper oven heating unit will be reduced to about 250 watts.

In the broil position shown in Fig. '7, common contact bar I12 is engaged by the movable contact I16 which permits currents to flow to the upper oven heating unit 56 which is connected to the common conductor I90 and to the movable conductor I84 which contacts the common contact bar I80 so that in .this position full voltage is applied to the upper oven heat-unit 55 for broilingpurposes. In this position all the other contacts are in open position.

By thisparticular heatingarrangement for the oven. the top heating coils .for both broiling and baking are evenly distributed over the top of the oven so that the heat at the top of the oven is evenl distributed over the entire top of the oven for both broiling and baking. This particular arrangement avoids using separate sections of the upper heating unit for broiling and baking pur poses. Obviously this particular arrangement provides improved broiling and baking conditions.

I have provided two similar heating units in the top and bottom of the oven. andI provide a baflle over the top of the lower heating unit to shield the lower shelves from the radiant heat andto providea gentle circulation of the warm air in the oven to make the heating of the oven much more uniform. This baffle is of a peculiar shape and is inclined upwardly from its center portion toward its outer edges. It is provided witha long downwardly flanged opening extending generallyfromfront to rear, in order to pro-.

vide a passage through which air from the upper portion of the oven may readily enter the space beneath the bailie. The lower heating unit is entirely covered by the bafile and surrounds the flanged opening in the bafiie. The upper heating unit I use at a maximum capacity for broiling, while for baking I use the lower heating unit at maximum capacity at the full voltage, and the upper heating unit I use at one-half voltage and in addition connect the upper heating unit in series with an external resistance which further reduces the actual voltage applied to the upper heating unit. The heating units are provided with an arrangement creating a greater heat intensity at their front and rear edges. By this arrangement I provide an even distribution of heat in the upper portion of the oven for either broiling or baking. I also provide a heating arrangement by which both upper and lower heaters are operatedat full voltage and operated at maximum capacity for rapid heating.

While the low intensity, distributed heat in the top of the oven is a great aid in providing uniform distrbution of heat, it is of primary importance that the lower oven heating unit be provided with properly distributed heatand be bafiledin the most efiicient manner. Referring now more particularly to Figs. 8 to 13, the lower heating element is shown as formed generally of an upper relatively flat general rectangular wire frame member 220 having a projecting portion at its rear edge which supports the electrical plug 222 for connecting the heating unit 58 to its plug receptacle 54. The heating unit 58 is also provided with a.lower general rectangular wire frame in the formof a loop 224 which is bent downwardly at its side edges so that it may be engaged within the slideways 226 and 223 provided upon opposite sides of the bottom of the oven shell for holding the lower heating unit in place.

Extendingbetween the front and rear portions of thewire frame members 220 and 224 are the channel members 230 which are formed of sheet steel. These channel members .230 include a web portion 232, upper and lower flanged portions 236. and 238, and these fiangedportions have their edges turned inwardly as designated by the reference characters 238and 240, so as to receive the rectangular insulating blocks 242 which are provided with central. apertures 244. These channel members 230 therefore form a slideway for these insulating blocks 242. At uniformly spaced distances each of the channel members is provided withna rectangular opening 246 which is just slightly wider than the insulating block. Each of these flanged openings registers with the opening in its respective insulating block 242. The edges of the openings 246 are pressed inwardly as designated by the reference characters 248 and 258 in order to locate the insulating blocks in place within the confines of the channel members so as to prevent lateral movement and to hold them in alignment with the apertures 246 in the web of the channels 230, the web 232 of the channels 285} are provided with rectangular notches 252 at each corner thereby leaving the protruding end portions 254 and 256 which are bent around the front and rear portions of the upper and lower wire frame members 220 and 224 which are provided with flatted portions or notches 258 in order to hold the channels in position.

The electric heating unit is provided with an electrical resistance heating element in the form of a coiled resistance wire having such a resist- 11 ance as to provide 2600 watts at 235 volts. This coiled resistance wire has its opposite ends connected to the plug 222 and is threaded through the insulating blocks 222. Itshould be, noted that the coiled resistance wire does not extend across from one side of the center to the other except in the front of the heater where a single coil of resistance wire extends from one side to the other in order to connect the two sides in series with each other. It should be noted that the resistance wire is not coiled uniformly but that a single pass adjacent the rear edge of the heater on either side of the plug 222 and designated by the reference characters 266 and 262 is coiled considerably closer together than the portion 266 and 268 of the resistance wire in between the portions 266 and 262 and the portion 264. This last mentioned portion 264 is closely coiled like the portions 266 and 262 and extends completely across the heater from one side to the other at its front edge and forms the connecting pass between the two sides of the heater.

The coils of wire are so stretched that the portion of the coil between the portion 266 and the portion 264 has a resistance of about 7.4 ohms and likewise the portion between the closely coiled portion 262 and the closely coiled portion 264 also has a resistance of about 7.4 ohms. The portion 264 has a resistance of about 5.3 ohms and the portions 266 and 262 each have a resistance of about 2.6 ohms. It will therefore be seen that the heat intensity is concentrated at the front and rear edges of the heating unit where the greatest amount of heat is desired in order to obtain substantially uniform. temperature conditions throughout the oven. Thus in order to secure the desired distribution of heat intensity, the portions 266, 262 and264 have their coils only about one-half as far apart as, the portions 266 and 268 which are located between the closely coiled portions. Thus I provide a distribution wherein about 20% of the heat is provided at the front and substantially the same proportion at the rear edge of the heater and slightly less than 60% of the heat is provided in between the frontand rear edges.

In order to provide a satisfactory distribution of heat from the lower heating unit 58 I provide the baffle 66 directly above it. This bafile is supported by four supports 216 which are fastened to the front and rear edges of the bafile 66 adjacent the corners and extenddownwardly and are fastened to the front and rear edges of the upper wire frame member 226. This bafile 66 has its outer edges 212 curled downwardly a small distance providing a reinforcement for its edges and at its center portion it is provided with a deeply flanged aperture 214 which is flanged downwardly a considerable distance very nearly to the level of the coiled resistance wire. The baffle 66 slopes upwardly on either side of the long flanged aperture 214 at a uniform slope of about This baflie provides a means of protecting the food on the lower shelves of the oven from obtaining too much radiant heat from the lower heating unit. Thus this bafile serves as a shield since it completely covers the portions of the heating unit which contain the coiled resistance wire.

It also serves as a means to promote a gentle .evenly distributed circulation. Thus the uniform slope of the baffle on each side of the flanged aperture 214 produces a circulation of warm air laterally under each side of the baffle and upwardly along the side walls and then to distribute itself through the interior of the oven. The flanged aperture 214 provides a means by which the air when slightly cooled may be returned to the lower heater beneath the bailie. The deep flange of the flanged aperture 214 tends to prevent. to a certain extent, any warm air from passing upwardly through it instead of passing laterally beyond the side edges of the bafiie. I find that this deeply flanged aperture in the center of the bafiie increases the rate of circulation over baffles which have previously been used thereby avoiding the trapping of heat beneath the baille, and thus provides a much more even distribution of heat in the oven. This baflie is not only useful with the two unit type of oven shown in the drawings, but may also be used with the single unit type of oven where space is provided for b-roiling beneath the lower heating unit.

As mentioned before the upper heating unit 66 is identical to the lower heating unit 66 excepting that it is inverted. It is supported in slideways 216 and 218 provided upon the top wall of the oven, which slideways are similar to the slideways 216 and 218 provided in the bottom. The increased heat intensity at the edges of the upper unit 56 provides much better broiling conditions than prevails in other heating units and also provides better baking conditions. The sidewalls of the oven are provided with projections 286 which form supports and guides for the shelves 282. Thus by providing a lower oven heating unit with about 40% of its heating capacity located upon its front and rear edges and by providing this greatly improved form of baiile, and also by providing a properly distributed small amount of heat at the top of the oven I have'provided an oven which provides much more uniform heating than has heretofore been accomplished .with an arrangement of this type.

In Fig. 12 is shown a modified form of heating unit designated by the reference character 358 which is formed of the upper and lower rectangular wire frame members 326 and 326 which are provided with channel members 33!) extending from front to rear as in the heating unit 58. These channel members are constructed like the channel members of the heating unit 58. The coiled electrical resistance wire is threaded through the insulators supported by the channel members 366 in a fashion like that shown in Fig. 12. for the lower heating units 58.

This coiled resistance wire differs from that shown in Fig. 12 by having closely coiled portions 666 and 362 at the rear edge of the heating unit which extend not only across the rear edge of the heating unit but these closely coiled portions extend to form a loop upon the side of the heating unit. Connected to the closely coiled portions 366 and 362 are the loosely coiled portions 364 and 366 which form loops on the inner portions of the heating unit. These loosely coiled portions are then connected to closely coiled portions 368 and 316 which form loops at the outer edge of the heating unit. The resistance element then continues in alternate loosely coiled and closely coiled portions with the loosely coiled portions forming the inner loops, while the closely coiled portion-s form the outer loops until the front of the heating unit is reached, where a closely coiled portion 312 is provided which extends entirely across the front of the heating unit and also forms loops at the outer edges of the heating unit.

Thus with this form, the heating unit is provided with closely coiled portions at the front and rear as well as in the loops on the outer edges,

- nipulating arm .4030.

while the loops on the inner portions of the heating unit are loosely or widely coiled. This provides a greater amount of heat at all the edges of the heating; unit and a lesser amount of heat in the central portions of the heating unit. Thu-s this form creates more heat at the edges, and in this way provides more uniform temperature distribution which is advantageous for broiling as well as baking. This modified form of heating may be used like the heating unit 58 in either the single or two unitoven. It may be used with a similar bafile 340 provided with a deep downwardly flanged aperture 3M. It may also be used as the upper heating unit in connection with a lower heating unit like that of Fig. 12. If de sired, a diiferent bafile may be used or a different slope employed such as From the foregoing description of the oven heating system, it is to be seen that I have provided a system in which upper and lower oven electric resistance heater units are controlled by a unitary manual switch. The upper heater is primarily suitable for broiling purposes when applied to full voltage. The lower electric heater unit is primarily suitable for baking purposes when applied across the full voltage. I connect the heaters to electric supply means in such a manner that the upper heater ,unit is used alone across the full voltage for broiling purposes, while for baking purposes the upper heater unit is placed across a reduced voltage simultaneously energized with the lower heating unit with the full voltage across the lower unit.

,In the ioregoing description I have indicated how these oven heating units may be applied to a three-wire circuit; but other modifications are possible with both three-wire and two-wire circuits. ,Such modification-s are diagrammatically indicated in Figs. 14 to 19 inclusive.

In Fig. 14 the upper and lower heating units are shown at 56 and 58. A two-line source of electrical supply is indicated by the wires A90 and llll- A resistance 402 may be placed outside of the oven, and a multiple switch 483 with a single manual control is provided for regulating the energization of the oven units. The arrangement is such that switching mechanism 493 can disconnectthe units 56 and 58 completely from the source of supply, can place :both units across the full voltage for preheat, can place the lower unit SB-across the full voltage with the upper unit 55 across a reduced voltage for baking, and can place the upper .unit 56 alone across. the full voltage for b-roiling. The switch structure may be of any desired unitary construction such that the necessarycontacts can be manipulated from a single handle. This structure, for example, may include movable contacts 603a, 4831) interlocked by ma- When the movable contacts Mile and 46% are over stationary contacts 4M and 495, the switch is in the off position. At'this time the extension wad of arm 5.834: impinges upon, and opens, the switch lo'l thereby disconnecting both sides of the units 56 and 58 from the wires 4!!!) and .01. When movable con tacts 403a and 4333b are moved over stationary cont-acts 4G3 and 489,armextension 493d is moved away from switch 401 and switch 48'! closes, and the units 55 and 53 are placed across the full voltage in parallel across the wires dill} and 4M.

In this position of the switch, the units are at the maximum heating capacity and-are to be used for preheating the oven. When the movable contacts, are placed over the contacts 4H: and M I,

the switch 39'! remains closed, the lower unit 58 is across the full voltage, and the upper unit 56 is across a reduced voltage by being placed in series with the resistance 402. In this position the unit-s are suitably energized for baking. When the movable contacts are placed over the contacts 442 and M3, the switch remains closed, and the upper unit 5% alone is placed across the full voltage of the wires can and This is suitable for broiling.

If desired, an adjustable thermostat having a diaphragm or bellows 4M may be connected to a bulb M5 in the oven in such a manner that the expansion of the bellows M4 by the thermostatic liquid, such as chlorinated diphenyl, opens a switch, such as 401, When the oven reaches a predetermined temperature. By adjusting the impingement or contact screw M5, the operating distance of the bellows may be varied so that the opening temperature of the switch may be varied or selected to suit the user. Also, if desired, an electric clock mechanism may be provided which may be set to close the contacts 550; and 6% at a predetermined time and to open them at a later predetermined time, thus providing for an automatic baking operation of selected time and duration,

In Fig. 15 the oven units 56 and 53 are connected to a three-wire source including wires 42B, 42! and 422. This may be the usual threewire alternating current supply with wire 42! as the neutral wire. The arrangement is such that the switch structure 423 may place both units across the full voltage of wires 42:! and 422 for preheat, the lower unit 58 across the full voltage of wires 425 and 422, with the upper unit 56 across the reduced voltage between either of the line wires 426 or 422 and the neutral wire 42! for baking, and the upper unit '56 alone across the full voltage between the wires G20 and 422 for broiling. For example, when the movable contacts 323a and 42327 are placed over the stationary contacts @524 and 1 25 by manipulating interlock arm 4723c, arm extension 623d impinges on, and opens switch 426, so that the units 56 and 58 are completely disconnected from the live wires. When the movable contacts 423a and 4231) are placed over contacts 627 and 323 by means of manipulating interlock arm 423e, switch 426 is closed because extension 423d is retracted from switch 426. At this time, 'both units 56 and 58 are placed across the full voltage between wires 326 and 422 thus rendering them suitable for preheating the oven. When the movable contacts 423:! and 4231), are placed over contacts 429 and 4232, switch 428 remains closed and the lower unit 53 is placed across the full voltage between line 428 and line 422 with the upper unit across the reduced voltage between the lines 42!! and AM. The units are suitably energized for baking in this position. When the movable contacts 423a and 62% are placed. over the contacts 63l and 5 32, switch 42% remains closed and the upper unit 55 alone is placed across the -full voltage of lines 320 and 422 and is suitably energized for broiling. In this modification also, a thermostat 433 is provided similar in function, adjustment etc, to the thermostat shown in Fig. 14. The clock mechanism 65 may also be provided.

In Fig. 16 an arrangement is shown for energizing the units 56 and 58 by means of the two- Wire source 4% and 44!, utilizing an autotranformer 442. When the switch structure M3 is placed with its movable contacts 443:; and l-13b over contacts M4 and 445, the system isin the .ofi position, with the switch 4% opened by extension 443d of interlock 4630 and with the units 56 and 58 completely disconnected from the electrical supply. When the movable contacts 443a and me are placed over contacts 34'! and 448, the switch 445 is closed, and the units 55 and 58 are placed in parallel across the full voltage of lines 448 and Ml and are suitably energized for preheating. When the movable contacts 443a and 443?) are placed over contacts 549 and 45d, switch 446 remains closed, lower unit 58 is placed across the full voltage of lines 448 and 44!, and the upper unit 56 is placed across a reduced voltage extending from the line 548 to a selected point in the autotransformer 442. The units are suitably energized for baking in this position. If desired, autotransformer 442 may be made adjustable so that any desired energization of the upper unit may be obtained. When the movable contacts 4 43a and 443b are over contacts 45| and 452, the upper unit 56 alone is placed across the full voltage of the wires 44!. and 44! and is suitably energized for broiling. A thermostat 453 may be provided, is similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock'mechanisrn 66 may also be provided.

In Fig. 17 the units 56 and 58 are connected to a three-wire source 46D, 46! and 452. In this arrangement a resistance 463 is placed adjacent to the lower unit 58, and may be built structurally integrally therewith. This resistance may be placed in series with the upper unit 56 across the reduced voltage of 469 and 46! when the switch arrangement about to be described is placed in the bake position. When the mov able contacts 464a and 4641) of the switch structure 464 are placed over the contacts 465 and AG? by means of the manipulating interlock 4540, the switch 468 is opened by arm extension 454d and the switch structure is in the ofi position completely disconnecting the units 56, 58 and 463 from the electric source of supply. When the movable contacts 464a and 4M1? are placed over the contacts 469 and m, the switch '468 is closed and the units 56 and 58 are placed across the full voltage of lines 46% and 562 and are suitably energized for preheating the oven. When the movable contacts 464a and 46% are placed over the contacts 4' and M2 the lower unit 58 is placed across the full voltage 460 and 352 while the upper unit 56 is placed in series with the resistance 4E3 across the reduced voltage 460 and 45!. This is suitable energization for baking. When the movable contacts 464a and 454i: are placed over contacts 413 and 4'54, the upper unit 55 alone is placed across the full voltage of lines 46!.) and 662 and is suitably energized for broiling. A thermostat 415 is provided, which may be similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 68 may also be provided.

In Fig. 18, the units 56 and 58 are connected to a two-wire source 48! and 48!. A resistance 4&3 may be provided adjacent to, and if desired integrally built into, unit 58. When the movable contacts 484a and 4841) of the switch structure 554 are placed over the contacts 485 and 486 by the manipulating interlock arm 4340, switch 48'! is opened by the extension 484d and the arrangement is in the off position with all of the units completely disconnected from the electrical supply. When the movable contacts 484a and 4841) are over contacts 488 and 539, switch 481 is closed and both units 58 and 55 are placed in parallel across the full voltage 480 and 48! and are suitably energized forpreheating the oven. When the movable contacts 484a and 48417 are placed over contacts 498 and 49 i the lower unit is placed across the full voltage Md and 43! with the upper unit 56 placed in series with the resistance 483 across 480 and 4M to impose a reduced voltage on the unit 55. The units are suitably energized for baking in this position. When the movable contacts ts a and 484?) are placed over contacts 492 and 493 the upper unit 56 alone is placed across the full voltage 488 and 48! and is suitably energized for .broiling. A thermostat 494 may be provided similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 66 may also be provided.

In Fig. 19 the units 55 and 58 are connected with the two-wire source 5% and EDI. In this modification a reduced voltage is imposed on the upper unit 56 in the baking position by placing it in series with a portion of the lower unit 58, thus using a portion of the lower unit 58 as a resistance. When the movable contacts 562a and 50212 of the switch structure 502 are placed over the contacts 503 and 504 by the manipulating interlock 5020, the switch 565 is opened by extension 592d and the units 5t and 58 are completely disconnected from the source of electrical energy, the switch structur being in the off position. When themovable contacts 502a and 50212 are placed over contacts 5% and 5M, switch 502 is closed, the units 55 and 58 are placed across the full voltage 58d and Sill and are suitably energized for preheating the oven. When the movable contacts 582a. and 59th are placed over contacts 508 and 509, the lower unit 58 is placed across the full voltage 53%) and 5!]! while the upper unit 56 has a reduced voltage imposed on it by placing it in. series with a portion of the lower unit 58 across the lines 500 and 50 i. This suitably energizes the units for baking. When the movable contacts 5532a and 58217 are placed over contacts 5m and 5!! the upper unit 56 alone is placed across the full voltage 5&0 and 58! and is suitably energized for broiling. Athermostat M2 is provided which is similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 66 may also be provided.

In the description of Figs. 14, 16, l'land 18, a two-wire source has been referred to; but it is understood that this two-wire source may be two selected wires of a three or more wire source.

Referring more particularly to Figs. 20 and 21, the switch shield 32 and the U-shaped channel 34 provide a protected conduit under the cover 22 for the wires 84a, 86a, 36a, and 8311 leading from the switches 34, 86, 36 and 88 and terminating centrally with respect to the surface heaters 26 so that the wires may be flexibly connected to the respective heaters 25 as indicated. This protects the wires from spillage, and at the same time allows the heaters 25 to be lifted or tilted from the cover 22 a sufficient distance for cleaning the heaters and stove. The U-shaped channel 34 prevents the wires from moving under the surface heaters where they might be damaged by spillage. The unenergized portions of the heaters 26 may be grounded to the channel 34 by wires 26a.

The switch channel 38 may be covered by an enameled plate 3811, through which the switch stems 38b extend. Switch knobs 380 are pushed on the stems 381).

While the forms or embodiment oi the. inven- 17 tion as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow:

What is claimed is as follows:

1. A domestic electric range having an oven provided with substantially similar upper and lower electric resistance heating units extending substantially across the top of the oven and across the bottom of the oven with a food space between said heaters, shelving in said food space between said heaters, an external resistance outside said oven, 2. line terminal block to be connected to a three-wire electrical supply source having two main wires and a third wire to provide a relatively high voltage across said two main wires and a relatively low voltage between said two main wires and said third wire, manual switch means operated by a single manipulating device, cables connecting said terminal block, manual switch means and electric resistance heating units, said manual switch means having one position connecting the upper heater unit across said relatively high voltage to energize said upper heater unit at full capacity for broiling purposes, in another position connecting said upper heater unit and external resistance in series across said relatively low voltage to energize said upper heater unit at substantially less than one-fourth its full capacity with said lower heater unit across said relatively high voltage to energize said lower heater unit at full capacity for baking purposes, and in another position with both said heaters in parallel across said full voltage to energize both of said heaters at full capacity for preheating purposes.

2. A stove oven system comprising; an oven, an electrical broiling heater in the upper part of the oven, an electrical baking heater, an external resistance, switch means connectible to said heaters and external resistance and adapted to be connected to a three-wire source of power having two live lines and a neutral line, said switch means having a single knob for connecting both of said heaters across the live lines for preheating, for connecting said electrical baking heater across said live lines and electrical broiling heater across one of said live lines in series with said resistance to said neutral line, and for connecting said upper electrical broiling heater alone across said live lines.

3. An electrical oven heating system for domestic use comprising a three-wire source having a relatively high voltage across two 01 said wires as compared with that across each of said two wires and a third wire, an upper oven heating unit above the food heating space of the oven, a lower oven heating unit below the food heating space of the oven, external resistance, connecting means for connecting said upper oven heating unit alone across said two wires for broiling purposes, and for connecting said lower oven heating unit across said two wires and said upper heating unit in series with said external resistance across one of said two Wires and the third wire for baking purposes.

4. A stove oven system comprising; an oven having a food heating space, an electrical broiling heater in the upper part of the oven above said space, an electrical baking heater in the lower part of said oven below said space, an external resistance, switch means connectible to said heaters and external resistance and adapted to be connected to a, three-wire source of power having two live lines and a neutral line, said switch means having a single knob for connecting both of said heaters across the live lines for preheating, for connecting said electrical baking heater across said live lines and electrical broiling heater across one of said live lines in series with said resistance to said neutral line, and for connecting said upper electrical broiling heater alone across said live lines.

FRANCIS H. McCORMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,154,416 Kuhn Sept. 21, 1915 1,416,009 Forshee May 16, 1922 1,652,120 Holbrook Dec. 6, 1927 1,683,196 Kempton Sept. 4, 1928 1,813,427 Rutenber July 7, 1931 1,816,866 Patterson Aug. 4, 1931 1,827,656 Heinbuch Oct. 13, 1931 1,911,383 Noble May 30, 1933 2,000,343 Lusher May 7, 1935 2,000,413 Myers May 7, 1935 2,035,767 Schulze Mar. 31, 1936 2,055,246 Bradbury Sept. 22, 1936 2,064,634 Sharp Dec. 15, 1936 2,142,381 Sickinger Jan. 3, 1939 2,203,236 Randolph June 4, 1940 2,314,592 McCormick Mar. 23, 1943 

